Unable to amend clients detail and penalise client

After a bank change, i contact Cell C to amend my bank details for the debit order, at the beginning of June, at the end of June they had not yet changed my details on their system, so the debit order was taken off my old bank, which bounced, i contacted Cell C to again refer them to my new details, i then did a transfer on the same day for the months account. this month again they tried to debit my old bank for the amount due, which again bounced. i contacted the call centre on sat 25th around 20:20 and was told that my new bank IS loaded and not the old one, no matter how many times i mentioned that the old bank was still being debited. after being placed on hold for numerous occasions, i was told yes sorry the old bank was still loaded and that they will update the details now. however due to the incompetence of the call centre staff i was penalised with R70 that was added onto my bill for July (due to late payment) even though id previously contacted the call centre, and paid long before the end of the month, i am guessing that i will again be penalised this month due to their incompetence. i am still waiting for a call centre supervisor to contact me since sat to resolve!!!